1. Field of the Invention
The present invention relates to a passenger detecting system and an air bag apparatus. More particularly, the present invention relates to a technique for detecting the presence or absence of a passenger in a seat of an automobile and for controlling the expansion of an air bag of an air bag apparatus.
2. Description of the Related Art
Generally, an air bag apparatus is an apparatus to ease the impact which a driver and passengers receive upon collision of an automobile. The air bag apparatus has been necessary for the safety of the automobile. Recently, the air bag apparatus has been installed at the passenger side in addition to the driver""s side.
For example, as shown in FIG. 1A; a first conventional air bag apparatus is composed of a driving seat side squib circuit, a passenger seat side squib circuit, an electronic acceleration sensor GS as a collision detecting sensor, and a control circuit CC. The driving seat side squib circuit includes a series circuit of a safing sensor SS1; a squib SQ1, and a switching element SW1 such as an electric field effect type transistor. The passenger seat side squib circuit includes a series circuit of a safing sensor SS2, a squib SQ2, and a switching element SW2 such as an electric field effect type transistor. The control circuit CC has a function to detect collision of an automobile in accordance with the output signal of the electronic acceleration sensor GS and to supply a signal to the gates of the switching elements SW1 and SW2.
According to the first conventional air bag apparatus, in the event of an automobile collision, the switch contacts of the safing sensors SS1 and SS2 are closed in response to the relatively small acceleration. Then, the squib circuits on the driving seat side and the passenger seat side are set to their operable states. When the control circuit CC reliably determines the collision of the automobile in accordance with the signal from the electronic acceleration sensor GS, squib control signals are supplied to the gates of the switching elements SW1 and SW2 to set to the ON state. By this, a current flows through each squib circuit. As a result, the squib circuits SQ1 and SQ2 are heated and the air bags on the driving seat side and the passenger seat side are developed, so that the driver and passenger are protected from the impact of the collision.
In the first conventional air bag apparatus, the air bag is expanded out upon collision of the automobile irrespective of whether or not a passenger is present in the passenger seat or of the size of the passenger. For example, when an adult passenger is present in the passenger seat, the passenger will be protected upon the collision as mentioned above. However, when the passenger is a child, since a child is shorter than an adult, the head position of the child is low than that of the adult. Therefore, there is a concern of injury to the child during expansion of the air bag a child, it is sometimes desirable that the air bag is not expanded even if the automobile collides.
Therefore, a second conventional air bag apparatus as shown in FIG. 1B has been proposed to cope with such a problem. In this air bag apparatus, a sensor SD is further provided to detect whether or not a passenger is present in a passenger seat. The control circuit CC determines whether or not a passenger is present in the passenger seat in accordance with a detection signal of the sensor SD, and selectively sets the air bag to either the expansion allowable state or the expansion inhibited state in accordance with the determined result.
In particular, a passenger detecting system using a weight sensor such as the sensor SD is proposed in which the determination of whether the passenger is an adult or a child is performed in accordance with the weight of the passenger as measured by the weight sensor. Also, a passenger detecting system is proposed in which an image of the passenger in the passenger seat is picked up by a camera and a determination of whether the passenger is an adult or a child is performed through image processing.
According to the former system, a rough determination of whether the passenger is an adult or a child is possible. The air bag is set to either the expansion allowable state or the expansion inhibited state in accordance with the determination result. Thus, the unexpected situation in a collision of an automobile can be avoided. However, there is a problem of a lack of accuracy, because the difference in weight between individuals is large and a child can be sometimes heavier in weight than an adult.
Also, according to the fatter system, the determination of whether or not a passenger is present in the seat, and the determination of whether the passenger is an adult or a child can be quite correctly performed. However; there is a problem in that a processor for determining the above-described information becomes complicated and expensive, because the imaging data picked up by the camera needs to be subjected to image processing and a comparing process with various image patterns.
In conjunction with the above, a passenger detecting system to detect the presence or absence of a passenger in the passenger seat are proposed in various systems. In Japanese Laid Open Patent Application (JP-A-Heisei 4-46843), Japanese Laid Open Utility Model Application (JP-U-Heisei 3-52266), Japanese Laid Open Patent Application (JP-A-Shown 61-113527), a passenger detecting system in which a weight sensor is incorporated inside the seat is disclosed. Also, Japanese Laid Open Patent Application (JP-A-Heisei 9-509118)discloses a passenger detecting system in which electrodes are arranged in a seat section and a back supporting section of a seat and an-oscillation circuit is connected between the electrodes or between the electrode and the chassis of a vehicle.
Therefore, an object of the present invention is to provide a passenger detecting system in which the presence or absence of a passenger in a seat can be accurately detected irrespective of an ambient temperature.
Another object of the present invention is to provide a passenger detecting system in which the presence or absence of a passenger in a passenger seat can be accurately detected without influence by the position of the passenger.
Still another object of the present invention is to provide an air bag apparatus which includes the above passenger detecting system and in which an air bag can be controlled in accordance with detected result.
In order to achieve one aspect of the present invention, a passenger detecting system includes an antenna electrode, a signal generating circuit, a detecting circuit, and control circuit. The antenna electrode is provided in a seat to be occupied by a passenger. The signal generating circuit generates and supplies a supply signal to the antenna electrode through a resistor such that an electric field is generated around the antenna electrode. The detecting circuit includes the resistor, and detects direct current data signal from a line voltage associated with a voltage drop by the resistor, wherein the line voltage changes depending upon an object on the seat. The control circuit determines from the detected direct current data signal, whether or not a passenger is present on the seat and whether the passenger is an adult or a child.
The passenger detecting system may further include an amplitude control circuit for detecting an amplitude of the supply signal and adjusting the amplitude to a predetermined value based on the detected amplitude. The supply signal may be an alternating current signal having a frequency of about 120 KHz and a voltage in a range of 5 to 12 V.
The detecting circuit may include a converter for converting the line voltage of alternating current into a direct current signal. In this case, the detecting circuit further includes an impedance converting circuit provided between the resistor and the converter and having a high impedance on an input side and a low impedance on an output side.
The detecting circuit may include a rectifier for rectifying the line voltage of alternating current into a direct current signal in full wave, and a smoothing circuit for producing the direct current data signal from the direct current signal.
Also, the detecting circuit may include a rectifier for rectifying the line voltage of alternating current into a direct current signal in half wave, and a smoothing circuit for producing the direct current data signal from the direct current signal. In this case, the rectifier includes an operation amplifier having an inversion terminal connected to a predetermined voltage and a non-inversion terminal connected to the line voltage.
The passenger detecting system may further include a buffer circuit provided between the resistor and the antenna electrode and having a high impedance on an input side and a low impedance on an output side.
When the signal generating circuit supplies the direct current supply signal, the detecting circuit may include a switching element connected between the resistor and a ground level for switching between an on state and an off state in response to a control signal from the control signal such that a pulse signal is supplied to the antenna electrode.
The passenger detecting system may further include a plurality of antenna electrodes; and a switching circuit provided between the resistor and the plurality of antenna electrodes, and selectively supplying the supply signal to one of the plurality of antenna electrodes in response to a switching control signal from the control circuit.
Alternatively, the passenger detecting system may further include a plurality of antenna electrodes, a plurality of circuit sets respectively provided for the plurality of antenna electrodes, each of the circuit sets including a signal generating circuit and a detecting circuit, and a switching circuit provided between the control circuit and the plurality of circuit sets, and selectively supplying the control signal to one of the plurality of circuit sets in response to a switching control signal from the control circuit.
The control circuit may: produce signal data from the detected direct current data signals corresponding to the plurality of antenna electrodes, calculate a summation of the signal data, determine, based on the summation of the signal data, whether or not a passenger is present in the seat.
Alternatively the control circuit may producesignal data from the detected direct current data signals corresponding to the plurality of antenna electrodes; calculate a summation of the signal datadeterninedetermine based on the summation of the signal data, whether or not a passenger is present in the seat; normalize each of the signal data based on a maximum one of the signal datacalculate a summation of the normalized signal datadetermine, based on the summation of the normalized signal data, whether the passenger is an adult or a child. In this case, the control circuit further calculates a gravity of the normalized signal data, and determines, based on the summation of the normalized signal data and the calculated gravity, whether the passenger is an adult or a child.
In order to achieve another aspect of the present invention, an air bag apparatus includes a passenger detecting system and an air bag control system. The passenger detecting system includes an antenna electrode, a signal generating circuit, a detecting circuit and a control circuit. The antenna electrode is provided in a seat to be occupied by a passenger. The signal generating circuit generates and supplies a supply signal to the antenna electrode through a resistor such that an electric field is generated around the antenna electrode. The detecting circuit includes the resistor, and detects a direct current data signal from a line voltage associated with a voltage drop by the resistor, wherein the line voltage changes depending upon an object on the seat. The control circuit determines from the detected direct current data signal, whether or not a passenger is present in the seat and whether the passenger is an adult or a child. The air bag control system is connected to the control circuit and sets an air bag to either an expansion allowed state or expansion inhibited state based on the determination result by the control circuit.
The air bag apparatus may further include an amplitude control circuit for detecting an amplitude of the supply signal and adjusting the amplitude to a predetermined value based on the detected amplitude. Also, the supply signal may be an alternating current signal having a frequency of about 120 KHz and a voltage in a range of 5 to 12 V.
The detecting circuit may include a converter for converting the line voltage of alternating current into a direct current signal. The detecting circuit may further include an impedance converting circuit provided between the resistor and the converter and having a high impedance on an input side and a low impedance on an output side. Further, the detecting circuit may include a rectifier for rectifying the line voltage of alternating current into a direct current signal in full wave, and a smoothing circuit for producing the direct current data signal from the direct current signal. Alternatively, the detecting circuit may include a rectifier for rectifying the line voltage of alternating current into a direct current signal in half wave, and a smoothing circuit for producing the direct current data signal from the direct current signal. In this case, the rectifier includes an operation amplifier having an inversion terminal connected to a predetermined voltage and a non-inversion terminal connected to the line voltage.
The air bag apparatus may further include a buffer circuit provided between the resistor and the antenna electrode and having a high impedance on an input side and a low impedance on an output side.
When the signal generating circuit supplies the supply signal of a direct current, the detecting circuit includes a switching element connected between the resistor and a ground level for switching between an on state and an off state in response to a control signal from the control circuit such that a pulse signal is supplied to the antenna electrode.
The air bag apparatus may further include a plurality of the antenna electrodes, and a switching circuit provided between the resistor and the plurality of antenna electrodes, and selectively supplying the supply signal to one of the plurality of antenna electrodes in response to a switching control signal from the control circuit.
Alternatively, the air bag apparatus may further include a plurality of antenna electrodes, a plurality of circuit sets respectively provided for the plurality of antenna electrodes, each of the circuit sets including a signal generating circuit and a detecting circuit, and a switching circuit provided between the control circuit and the plurality of circuit sets, and selectively supplying the control signal to one of the plurality of circuit sets in response to a switching control signal from the control circuit. In this case; the control circuit produces signal data from the detected direct current data signals corresponding to the plurality of antenna electrodes, calculates a summation of the signal data, and determines, based on the summation of the signal data, whether or not a passenger is present in the seat.
Alternatively, the control circuit produces signal data from the detected direct current data signals corresponding to the plurality of antenna electrodes, calculates a summation of the signal data, determines, based on the summation of the signal data, whether or not a passenger is present on the seat, normalizes each of the signal data based on a maximum one of the signal data, calculates a summation of the normalized signal data, and determines, based on the summation of the normalized signal data, whether the passenger is an adult or a child. In this case, the control circuit may further calculate a gravity of the normalized signal data, and determines, based on the summation of the normalized signal data and the calculated gravity, whether the passenger is an adult or a child.